多壁碳纳米管的球磨处理对其吸附储氢性能的影响

研究了球磨改性对多壁碳纳米管储氢性能的影响,球磨处理前后的碳纳米管微观结构采用TEM和XRD进行表征. 结果发现,球磨处理能使碳纳米管长度变短,管端口打开,缺陷增多,表面积增大,球磨处理12 h的碳纳米管的吸附量从未球磨的1.60%(w)提高到2.55%(w),表明球磨改性能明显提高碳纳米管的吸附量.     

Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters

Multi-walled carbon nanotubes (MWNTs) with different mean outer diameters in the range of 13-53 nm, synthesized by the catalytic decomposition of hydrocarbons using a floating catalyst method, were purified and pretreated with the same procedure for volumetric hydrogen adsorption/desorption measurements. It was found that the hydrogen storage capacity of the purified and pretreated MWNTs was proportional to their diameter, and that hydrogen in all types of MWNTs measured could not be completely desorbed at room temperature and ambient pressure. A possible mechanism for the above behavior was proposed based on the results of cryogenic nitrogen adsorption analysis and high-resolution transmission electron microscopy observations. It was considered that small “carbon islands” might be the main hydrogen adsorption site in MWNTs. The effects of metal catalyst as well as an etched cavity on the surface of MWNTs on the hydrogen adsorption/desorption of MWNTs were also discussed.     

不同处理方式对竹节状碳纳米管吸氢量的影响

Bamboo-like carbon nanotubes were prepared by decomposing C_2H_2 on ferric catalyst. Acid immersion, ball milling and KOH etching were performed before hydrogen adsorption measurement. TEM, HREM, SEM and IR analyses were used to characterize the microstructure. The maximum hydrogen adsorption capacity of the raw sample reached 1.53% (mass) at 300 K under 7 MPa. The unusual structure of carbon nanotubes plays a dominant role for hydrogen adsorption. But some treatments will destroy the structure and decrease hydrogen uptake capacity.     

球磨改性热解炭吸附磺胺甲唑

针对热解炭颗粒大、表面活性弱、吸附能力差的问题,本文提出了一种机械球磨表面改性方法,探讨了不同球磨改性参数下热解炭对磺胺甲唑（SMZ）的吸附效果。以废橡胶连续热解炭为原料,采用不锈钢球磨制得具有不同表面性质的球磨炭,分析了球磨前后热解炭的结构、表面性质及表面形貌,并对比了球磨改性前后的SMZ吸附性能。结果表明,球磨改性过程可以有效改善废轮胎热解炭结构及表面性质,球磨处理2h的热解炭对SMZ的吸附效果最好,吸附量达到59.37mg/g,吸附动力学符合伪二级吸附模型。     

The role of carbon nanotube structure in purification and hydrogen adsorption

Structural properties of carbon nanotubes were studied by using samples from various manufacturers synthesized by different processes. A two-stage purification method was applied to all samples. Relationships between synthesis techniques and carbon nanotube structure are discussed. The role of carbon nanotube structural features such as degree of crystallinity, tube diameter, tube wall structure, and bundling behavior in purification and hydrogen adsorption were investigated by a combination of transmission electron microscopy and magnetic resonance techniques. It is suggested that MWNTs with low crystallinity and SWNTs with large diameters and open tube ends yielded the highest hydrogen uptake capacities. Both MWNTs and SWNTs show low hydrogen storage capacities (less than 1 wt%) at hydrogen pressures up to 1480 kPa.     

Synthesis and characterization of double-walled carbon nanotubes from multi-walled carbon nanotubes by hydrogen-arc discharge

Double-walled carbon nanotubes (DWNTs) were synthesized in a large scale by a hydrogen arc discharge method using graphite powders or multi-walled carbon nanotubes/carbon nanofibers (MWNTs/CNFs) as carbon feedstock. The yield of DWNTs reached about 4 g/h. We found that the DWNT product synthesized from MWNTs/CNFs has higher purity than that from graphite powders. The results from high-resolution transmission electron microscopy observations revealed that more than 80% of the carbon nanotubes were DWNTs and the rest were single-walled carbon nanotubes (SWNTs), and their outer and inner diameters ranged from 1.75 to 4.87 nm and 1.06 to 3.93 nm, respectively. It was observed that the ends of the isolated DWNTs were uncapped and it was also found that cobalt as the dominant composition of the catalyst played a vital role in the growth of DWNTs by this method. In addition, the pore structures of the DWNTs obtained were investigated by cryogenic nitrogen adsorption measurements.     

MnO2/MWNTs纳米材料的制备及对Cu（Ⅱ）吸附的研究

采用液相氧化还原法制二氧化锰/多壁碳纳米管(MnO2/MWNTs)复合材料,通过扫描电子显微镜(SEM)观察MnO2在MWNTs表面的负载情况,X射线衍射仪(XRD)显示MnO2是以无定形态排列在MWNTs表面。MnO2/MWNTs相比于MWNTs对Cu(Ⅱ)吸附能力提高了100%,MnO2最优负载量为30%,吸附过程的前10 min达到平衡吸附量的70%,80 min达到吸附平衡。温度升高有益于吸附。pH对吸附影响很大,吸附量随着pH的上升而增加,对Cu(Ⅱ)脱除率甚至达到了95.31%。     

碳纳米管负载纳米MnO2复合材料对Pb2+吸附的研究

采用液相氧化还原法制备MnO2/MWNTs复合材料,通过SEM(扫描电子显微镜)观察MnO2在MWNTs表面的负载情况,XRD(X射线衍射仪)显示MnO2是以无定形态排列在MWNTs表面。吸附过程的前10分钟达到平衡吸附量的70%,80min达到吸附平衡,温度升高有益于吸附,pH值对吸附影响很大,吸附量随着pH值的上升而增加,对Pb2+脱除率甚至达到了95.31%。     

Composite anode material of silicon/graphite/carbon nanotubes for Li-ion batteries

A composite anode material of silicon/graphite/multi-walled carbon nanotubes (MWNTs) for Li-ion batteries was prepared by ball milling. This composite anode material showed a discharge capacity of 2274 mAh/g in the first cycle, and after 20 charge-discharge cycles, a reversible capacity of 584 mAh/g was retained, much higher than 218 mAh/g for silicon/graphite composite. It was observed that silicon particles were homogeneously embedded into the “lamellar structures” of flaked graphite particles, and the silicon/graphite composite particles were further wrapped by a MWNTs network. The improvement in the electrochemical properties of the composite anode material was mainly attributed to the excellent resiliency and good electric conductivity of the MWNTs network.     

碳纳米管在氟碳树脂中的分散及其对光学性能的影响

采用球磨分散工艺制备了碳纳米管乙酸丁酯分散液,研究了分散剂的用量及分散时间对碳纳米管分散效果的影响.向上述分散液巾加入氟碳树脂制备成涂料,用扫描电子显微镜观察了碳纳米管在氟碳树脂中的分散状态,考察了分散状态对涂层热性能及光学性能的影响.     

海藻酸钠复合凝胶球的制备及其吸附性能研究

利用机械搅拌和超声波辅助法将多壁碳纳米管(MWNTs)分散于海藻酸钠(SA)水溶液中,然后将混合溶液滴入CaCl2水溶液中,制备了具有高吸附性的复合凝胶球(SA/MWNTs-Ca),研究了包埋不同含量MWNTs的SA/MWNTs-Ca凝胶球对甲基橙(MO)溶液的吸附脱色性能.结果表明:SA/MWNTs-Ca凝胶球对甲基...     

End morphology of ball milled carbon nanotubes

Multi-walled carbon nanotubes have been shortened by ball milling under ambient conditions. Detailed high-resolution TEM studies of the carbon nanotube ends showed a high-percentage of carbon nanotubes had partially or completely collapsed openings. Their stability was also discussed. Based on the morphology of the broken ends, different mechanisms for carbon nanotubes cleavage under ball milling conditions were proposed.     

Intrinsic linear scaling of hydrogen storage capacity of carbon nanotubes with the specific surface area

The linear scaling of the gravimetric hydrogen storage capacity of single- and multi-walled carbon nanotubes (SWNTs and MWNTs) with the specific surface area is investigated at ambient temperature (298 K) and technically relevant pressures (0.9–1.6 MPa). All samples are found to adsorb hydrogen reversibly and their adsorption exhibits type-II BET isotherms according to the IUPAC classification. While there is strong sample-dependency on their pressure–composition isotherms, all of them follow the Henry's Law in the pressure range under consideration. A comparison of the observed slope of specific surface area versus gravimetric storage capacity with that of a theoretically predicted one using a hypothetical condensation model and that of chemically modified carbon nanotubes revealed that the hydrogen storage capacity depends on the accessibility of internal surfaces of nanostructured carbon. The linear scaling of hydrogen storage capacity with the respective specific surface area suggests that the hydrogen adsorption in carbon nanotubes depends on the specific surface area and is irrespective of the type of the nanotubes that is used.     

低速球磨对多壁碳纳米管球磨特性的影响研究

利用低速球磨机对催化化学气相沉积法制备的多壁碳纳米管进行了球磨。透射电子显微镜实验结果表明。低速球磨机球磨可以使多壁碳纳米管开口和变短，球磨5h后碳纳米管开口和变短效果已经很明显；球磨20h后，发现碳纳米管变短到出现明显的团聚现象。X射线衍射实验结果表明，球磨20h后仍为多壁碳纳米管，每一层碳管仍为规则的石墨化结构。     

碳纳米管在金属间化合物中分散过程

采用超声分散结合机械球磨方法制备了均匀分散的多壁碳纳米管/Fe3Al金属间化合物复合粉体。利用透射电镜和红外吸收光谱对复合粉体的形貌和结构进行研究。透射电镜分析表明:藤状的碳纳米管缠绕着Fe3Al纳米颗粒,使Fe3Al纳米颗粒定向排列在一起。复合粉体的良好结合源于Fe—C键的形成。这种复合粉体有望提高金属间化合物的塑性和作为添加剂应用在复合材料中。     

Effect of activated carbons derived from different precursors on the hydrogen sorption properties of magnesium

The absorption-desorption characteristics towards hydrogen of obtained by ball milling under argon atmosphere magnesium based composites (containing respectively 95 wt% Mg and 5 wt% activated carbon (AC) derived from bean pods (BP), apricot stones (AS) and mixture of coal tar pitch and furfural (CTPF)), were investigated. Actually there is no substantial difference between the rate of hydriding and the absorption capacity for magnesium composite with AC derived from apricot stones, and for magnesium composite with AC derived from a mixture of coal tar pitch and furfural — the capacity is 6.13 wt% for the former and 5.98 wt% for the latter. More significant difference between the investigated composites was observed for the dehydriding process. The magnesium composite with synthetic carbon (from furfural and coal tar pitch) desorbs at 623 K and 0.15 MPa and the absorbed hydrogen about twice faster than magnesium composite with AC from bean pods. The activated carbon derived from a mixture of coal tar pitch and furfural has the highest specific surface area, and obviously this characteristic has important influence especially on the dehydriding kinetics of magnesium.     

The synthesis of functionalized carbon nanotubes by hyperbranched poly(amine-ester) with liquid-like behavior at room temperature

The solvent-free multi-walled carbon nanotubes (MWNTs) nanofluids are obtained through acid-base reaction and hydrogen bond roles with hyperbranched poly(amine-ester) (HPAE). MWNTs content is 16.8 wt%. The functionalized MWNTs exhibit liquid-like behavior in absence of solvent at room temperature. Correspondingly, the dense surface coverage is one modifying molecule per 30 carbon atoms on the surface of MWNTs. The functionalized MWNTs are soluble in good solvent of HPAE, but insoluble in non-solvent of HPAE. Their dispersibility, high thermal stability and ability to flow at room temperature make them attractive as lubricants, plasticizers and film-forming precursors.     

Hydrogen adsorption in different carbon nanostructures

Hydrogen adsorption in different carbonaceous materials with optimized structure was investigated at room temperature and 77 K. Activated carbon, amorphous carbon nanotubes, SWCNTs and porous carbon samples all show the same adsorption properties. The fast kinetics and complete reversibility of the process indicate that the interaction between hydrogen molecules and the carbon nanostructure is due to physisorption. At 77 K the adsorption isotherm of all samples can be explained with the Langmuir model, while at room temperature the storage capacity is a linear function of the pressure. The surface area and pore size of the carbon materials were characterized by N₂ adsorption at 77 K and correlated to their hydrogen storage capacity. A linear relation between hydrogen uptake and specific surface area (SSA) is obtained for all samples independent of the nature of the carbon material. The best material with a SSA of 2560 m²/g shows a storage capacity of 4.5 wt% at 77 K.     

KOH and NaOH activation mechanisms of multiwalled carbon nanotubes with different structural organisation

New information was obtained on the mechanism of porosity development during chemical activation by KOH and NaOH using various multiwalled nanotubes (MWNTs) of different structural organization. The high purity MWNTs were prepared by acetylene decomposition on a cobalt-based catalyst at different temperatures. The obtained samples ranged from MWNTs with well organised graphitic walls to nanotubes with disorganised layers mixed with some pyrolytic carbon when decreasing synthesis temperature. The results of transmission electron microscopy (TEM) observations were linked with gas adsorption measurements and X-ray diffraction data. They show that NaOH is only effective with disordered materials whereas KOH is effective whatever the structural order. After reaction of the poorly ordered precursor with KOH, the nanotubular morphology is completely destroyed, whereas it is preserved when NaOH is used. However for the more ordered materials, the morphology remains unchanged with both reactants. Effects of activation are only seen with KOH, which generated a large concentration of defects in the nanotubes walls. The differences found between KOH and NaOH during activation are related with an additional intercalation step of metallic K or Na produced during the redox reactions. It is shown that metallic K has the ability to be intercalated in all materials in contrast with Na which can only intercalate in the very disorganised ones. The conclusions obtained from the study on ordered nanotubes were confirmed with an ordered carbon black, demonstrating that the structural organization of the carbon precursor is an important parameter which must be taken into account when alkali reactants are used for the activation.